To withdraw blood for clinical analysis, a hollow needle sealed to a syringe is used to puncture the skin and an underling vein or artery. The plunger of the syringe is slowly withdrawn as the blood fills the evacuated space between the plunger and the barrel of the syringe.
The blood is then inserted into one or more sample tubes, which may contain any of a variety of preparations to further the particular analytical procedure, including anticoagulants, preservatives and the like.
An improvement over the syringe that is in wide general use is the evacuated glass tube sealed by a rubber stopper as illustrated in FIG. 1. A double-ended needle 1 is threadably engaged by threads 5 to needle holder 2. The glass tube 3, which may contain any of the preparations to enhance analysis, contains a vacuum and is sealed by rubber stopper 4. It is inserted into needle holder 2 until the first point 6 of the needle engages, but does not fully penetrate, the rubber stopper 4. The second needle point 7 is then forced through the skin into the blood vessel. The glass tube 3 is then pushed further into needle holder 2 so that it penetrates the stopper and applied the vacuum to the point 7 inside the blood vessel, aspirating blood into the tube. The tube 3 may be withdrawn from the holder 2 and one or more additional tubes may be used to collect additional samples for additional analyses that may require different chemicals within the tube. Care must be exercised in inserting and removing tubes while the needle is in the blood vessel so that the position of needle point 7 is not disturbed by forcing it through the other wall of the vessel or removing it from the vessel or moving it laterally as it may be dislodged from its effective position or may damage the blood vessel.
When sampling is completed, the needle point 7 is removed from the arm, a covering sheath, supplied with the needle, is reapplied to the point 7 and the needle is unscrewed from the needle holder 2 and discarded. Alternatively, the needle 1 and needle holder 2 are permanently joined together and are both disposed after a single use. The needle point of the disposable needle holder must also be sheathed prior to discard because of the dangers to users from accidental skin puncture from a needle contaminated with the blood of a person who may be infected with an infectious disease that is transmitted by just such a mechanism.